Intraluminal prostheses, such as stents, are generally known. Intraluminal stents may be deployed at a narrowed site in a body lumen, for example a blood vessel, to strengthen, support or repair the lumen. With angioplasty for example, implantations of stents have substantially advanced the treatment of occluded blood vessels. Once implanted, the prosthesis strengthens that part of the vessel such that blood flow is ensured.
Preferably, intraluminal stents have a small cross-sectional diameter and/or profile for introducing the stent into the affected body lumen. A configuration which is extremely suited for implantation in a body lumen is a generally cylindrical prosthesis which can radially expand from a first, small, collapsed diameter to a second, larger, expanded diameter. Such prostheses can be implanted in a body lumen by placing them on a catheter and transporting them through the lumen to the desired location. The prosthesis may be self-expanding or the catheter may be provided with a balloon or another expansion mechanism which exerts a radial outwards pressure on the prosthesis so that the prosthesis expands to a larger diameter.
One method of producing expandable intraluminal prostheses is by cutting a metal cannula around its circumference, for example to form a stent. Typically, the metal cannula is the size of the stent in its collapsed delivery state. Alternatively, the cannula is an intermediate size, between that of the collapsed diameter and expanded diameter of the stent.
Stents formed from an intermediate or collapsed size cannula may undesirably twist during expansion due to the stent's thin bars or struts. Another concern of intermediate or compressed-diameter cannula-formed stents is non-uniform radial expansion of the stent. Thin, flexible strut segments may not deform outwardly in the same manner and to the same degree as strut segments of higher radial strength, possibly resulting in stent segments extending or “hanging” into the lumen. Particularly in vascular stents, local blood flow turbulence can occur at these points that might contribute to thrombus formation. A design that increases longitudinal and radial strength and stability, and evenly distributes bending stresses is less prone to twisting and non-uniform expansion.
Still another consideration is stent migration following implantation due to physiological forces within the body lumen. Pulsatile flow is a major force that stents encounter; thus stents and endoluminal prostheses, if not properly anchored, may move downstream in the blood lumen in which they are placed. If the stents or endoluminal prostheses do migrate, their effectiveness may be diminished. To address migration, manufacturers may solder or otherwise bond outwardly-extending barbs or hooks to the prosthesis. However, non-integral barbs may deform or fracture from repeated physiological stresses, particularly the cyclical loading caused by cardiovascular pulsatile forces.